THE RIVER NILE
DR. S.M. ALAM
Aug 8 - 14, 2011
There are almost 200 small and big rivers flowing on the earth in different countries. The directions of flow of all these rivers are from north to south and finally into the seas or oceans.
The peculiarity of the 'River Nile' is that it is the only river on the earth which flows from the South direction to the North direction, and finally it enters into Mediterranean Sea near Alexandria, Egypt.
The River Nile is a major north-flowing river in North Africa, generally regarded as the longest river in the world. The Nile River is actually 6695 kilometers (4184 miles) long.
With such a long length, the Nile River is speculated to be the longest river in the world. The Amazon River runs a very close second, although it has been difficult to determine which is actually longer. River Nile facts state it winds from Uganda to Ethiopia, flowing through total nine countries.
While the Nile River is often associated with Egypt, it actually touches Ethiopia, Zaire, Kenya, Uganda, Tanzania, Rwanda, Burundi and Sudan as well as Egypt. It is only recently that the first known navigation team successfully followed the river from beginning to its end.
The Nile has two major tributaries, the White Nile and Blue Nile. The latter is the source of most of the water and fertile soil. The former is the longer. The White Nile rises in the Great Lakes region of central Africa, with the most distant source being as-yet undetermined, and located in either Rwanda or Burundi. It flows north through Tanzania, Lake Victoria, Uganda and southern Sudan. The Blue Nile starts at Lake Tana? / 12.03583; 37.26472 and flows into Sudan from the southeast. The two rivers meet near the Sudanese capital of Khartoum.
The northern section of the river flows almost entirely through desert, from Sudan into Egypt, a country whose civilization has depended on the river since ancient times. Most of the population and cities of Egypt lie along those parts of the Nile valley north of Aswan, and nearly all the cultural and historical sites of Ancient Egypt are found along riverbanks.
The Nile ends in a large delta that empties into the Mediterranean Sea. The source of the Nile is sometimes considered to be Lake Victoria, but the lake has feeder rivers of considerable size. The Kagera River, which flows into Lake Victoria near the Tanzanian town of Bukoba, is the longest feeder, although sources do not agree on which is the longest tributary of the Kagera and hence the most distant source of the Nile itself.
It is either the Ruvyironza, which emerges in Bururi Province, Burundi or the Nyabarongo, which flows from Nyungwe Forest in Rwanda. The two feeder rivers meet near Rusumo Falls on the Rwanda-Tanzania border.
The Nile leaves Lake Victoria at Ripon Falls near Jinja, Uganda, as the Victoria Nile. It flows for approximately 500 kilometers (300 mi) farther, through Lake Kyoga, until it reaches Lake Albert. After leaving Lake Albert, the river is known as the Albert Nile. It then flows into Sudan, where it is known as the Bahr al Jabal ("River of the Mountain"). The Bahr al Ghazal, itself 716 kilometers (445 mi) long, joins the Bahr al Jabal at a small lagoon called Lake No, after which the Nile becomes known as the Bahr al Abyad, or the White Nile, from the whitish clay suspended in its waters. When the Nile is flooded, it is left with a rich silt deposit, which fertilizes the soil. The Nile no longer floods annually since the completion of the Aswan Dam in 1970. An anabranch river, the Bahr el Zeraf, flows out of the Nile's Bahr al Jabal section and rejoins the White Nile.
The term "White Nile" is used in both a general sense, referring to the entire river above Khartoum, and in a limited sense, describing the section between Lake No and Khartoum. The flow rate of the Bahr al Jebal at Mongalla, Sudan is almost constant throughout the year and averages 37,000 cu ft/s.
After Mongalla, the Bahr Al Jabal enters the enormous swamps of the Sudd region of Sudan. More than half of the Nile's water is lost in this swamp to evaporation and transpiration.
The average flow rate of the White Nile at the tails of the swamps is about 18,000 cu ft/s. From here, it soon meets with the Sobat River at Malakal.
On an annual basis, the White Nile upstream of Malakal contributes about 15 per cent of the total outflow of the Nile River. The Bahr al Jebal and the Sobat River are the two most important tributaries of the White Nile in terms of discharge. The Bahr al Ghazal's drainage basin is the largest of any of the Nile's sub-basins, measuring 520,000 square kilometers (200,000 sq mi) in size, but it contributes a relatively small amount of water, about 71 cu ft/s annually, due to tremendous volumes of water being lost in the Sudd wetlands.
The Sobat River, which joins the Nile a short distance below Lake No, drains about half as much land, 86,900 sq mi, but contributes 412 cubic metres per second (14,500 cu ft/s) annually to the Nile. When in flood the Sobat carries a large amount of sediment, adding greatly to the White Nile's color.
The average flow of the White Nile at Malakal, just below the Sobat River, is 32,600 cu ft/s; the peak flow is approximately 43,000 cu ft/s in October and minimum flow is about 21,500 cu ft/s in April. This fluctuation is due to the substantial variation in the flow of the Sobat, which has a minimum flow of about 3,500 cu ft/s in March and a peak flow of over 24,000 cu ft/s in October. During the dry season (January to June), the White Nile contributes between 70 per cent and 90 per cent of the total discharge from the Nile.
Blue Nile springs from Lake Tana in the Ethiopian Highlands. The Blue Nile flows about 1,400 kilometers to Khartoum, where the Blue Nile and White Nile join to form the Nile. 90 per cent of the water and 96 per cent of the transported sediment carried by the Nile originates in Ethiopia, with 59 per cent of the water from the Blue Nile (the rest being from the Tekezé, Atbarah, Sobat, and small tributaries).
The erosion and transportation of silt only occurs during the Ethiopian rainy season in the summer, however, when rainfall is especially high on the Ethiopian Plateau; the rest of the year, the great rivers draining Ethiopia into the Nile (Sobat, Blue Nile, Tekezé, and Atbarah) have a weaker flow.
The Blue Nile contributes approximately 80-90 per cent of the Nile River discharge. The flow of the Blue Nile varies considerably over its yearly cycle and is the main contribution to the large natural variation of the Nile flow.
During the wet season the peak flow of the Blue Nile often exceeds 200,000 cu ft/s in late August.
During the dry season the natural discharge of the Blue Nile can be as low as 4,000 cu ft/s, although upstream dams regulate the flow of the river.
Before the placement of dams on the river the yearly discharge is varied by a factor of 15 at Aswan. Peak flows of over 290,000 cu ft/s would occur during late August and early September and minimum flows of about 19,500 cu ft/s would occur during late April and early May.